Patent Literature 1 discloses an abnormality detection device for detecting an abnormality in a hydraulic pump. The abnormality detection device of Patent Literature 1 includes a pressure detection section that detects a pressure of hydraulic fluid flowing out of the hydraulic pump in rotation, and a frequency analysis means that analyzes the pulsation frequency of the pressure of hydraulic fluid flowing out of the hydraulic pump based on pressures detected by the pressure detection section. The frequency analysis means analyzes the pulsation frequency of the pressure of hydraulic fluid flowing out of the hydraulic pump along the time axis. The abnormality detection device of Patent Literature 1 uses a result of the pulsation frequency analysis performed by the frequency analysis means to extract a waveform component of the rotation frequency of the hydraulic pump and determine whether the extracted component of the rotation frequency is a normal value or not, to thereby determine whether an abnormality occurs in the hydraulic pump.
As mentioned above, in the abnormality detection device of Patent Literature 1, the frequency analysis means analyzes the pulsation frequency of the pressure of hydraulic fluid flowing out of the hydraulic pump along the time axis, and a result of the analysis is used to determine whether an abnormality occurs in the hydraulic pump.
However, the pressure pulsation of hydraulic fluid changes depending on the rotation phase of the hydraulic pump. Therefore, there is a possibility that, in the abnormality detection device of Patent Literature 1, occurrence of an abnormality in the hydraulic pump cannot be accurately detected. When the pressure pulsation frequency of hydraulic fluid is analyzed along the time axis, the rotation speed of the hydraulic pump at the time of detection of a hydraulic fluid pressure by the pressure detection section needs to be always constant to maintain a constant relationship between pressure pulsation of hydraulic fluid and time. In other words, in the abnormality detection device of Patent Literature 1, the result of pulsation frequency analysis by the frequency analysis means changes according to the change in the rotation speed of the hydraulic pump and, therefore, there is a possibility that occurrence of an abnormality in the hydraulic pump cannot be accurately detected.